Just before lunchtime (BST) with the sun shining brightly, the shuttle vanishing high into the atmosphere and the clouds blocked all but the rain from the eyes down below here in Cumbria, something happened outside the magnetosphere, the region around the Earth where the terestrial magnetic field dominates over outside fields.
The solar wind suddenly started to ramp up its speed. Since then, we have been in the grip of a faster than usual solar wind stream. Why is this important? Because the effect of the solar wind altering its flow properties is that the magnetosphere of the Earth stretches and contracts and this releases the energy that powers the aurorae. This is the Dungey cycle.
Information from the ACE spacecraft (tweeted by Kav) showed a small rise in temperature and density of the solar wind petering out just before 1pm BST followed by a shift to southward interplanetary magnetic field (which is the type most likely to produce auroral activity) and a rise in solar wind velocity that peaked ninety minutes later at the highest we’ve seen for some time and only now is returning to normal. Aurora Alerts on twitter shows sudden rises in activity during both these events hitting a peak between 6.67-7 on the Kp index, indicating an aurora that (if timed right) would’ve been visible from down here in Kendal. But where did it come from?
Spaceweather.com mention that in the past 24 hours, the closest we’ve had to any flare activity was a B1 class x-ray flare (a slight cosmic hiccup that barely registers as noticeable). It does mention a large coronal hole (a region that isn’t producing many x-rays compared to the rest of the solar disc, but will be producing a stream of fast solar wind). They predicted its effects would hit tomorrow or the day after, but it looks like the fast solar wind has either arrived early or been preceded by an unseen small coronal mass ejection.
Either way, it looks like solar activity is heating up once more and we’ll be able to enjoy more frequent appearances of the Sun’s effect on the Earth at night.